TW202001979A - A plasma generating arrangement - Google Patents

Abstract

A plasma generating arrangement is disclosed. The arrangement comprises a plurality of plasma sources, each plasma source comprising a respective antenna coil assembly electrically coupled to a common electrical terminal via a respective transmission line. Each transmission line is configured to communicate a radio frequency electrical power signal from the common electrical terminal to the respective antenna coil assembly, and comprises a length which is an odd multiple of 1/4 of the wavelength of the radio frequency electrical power signal.

Description

Plasma production equipment

Field of invention The invention relates to a plasma generating device.

Background of the invention It is well known that plasma can be generated in a low-pressure plasma chamber by passing radio frequency current through an antenna disposed close to the process chamber. The antenna can be inside or outside the vacuum container depending on the plasma process requirements. This type of plasma can be used to etch, deposit, or treat surfaces near the plasma. The rapidly changing current generates a magnetic field that interacts with the gas in the chamber to generate plasma. So-called inductively coupled plasmas usually contain one or more radio frequency (RF) electrical power sources per chamber (or more if more than one RF frequency is required for the process) for generating current in individual antennas. Each RF power source is matched to the antenna impedance through the use of an RF matching network. The need to use a dedicated RF power supply and matching network for each antenna imposes constraints on the system designer. It would be desirable to be able to share an RF power supply operating at a fixed frequency (for example, 13.56 MHz) with multiple antennas to simplify system design, save space, and reduce costs.

In practice, when two or more RF antennas 10a, 10b used as excitation means for the low-voltage process chamber 15 are coupled in parallel with a single RF power supply 20, as shown in FIG. 1b, the resulting The magnetic field will be out of phase, and one of the coils 10a, 10b will become dominant and draw all electrical power from the source. However, this indicates that as the plasma 25 is local to the dominant coil, it is difficult to predict which coil will draw power to generate the plasma. The coil that becomes dominant can be judged by a slight difference in mechanical layout or gas conditions, but this is usually a random process. Similar results will occur when two or more separate chambers are driven in parallel from a single RF power supply.

Operating multiple antennas in close proximity on a single chamber 15 in series, for example, has limited benefits due to the interaction of the generated electromagnetic fields. For example, referring to FIG. 1a, if two coils 10a, 10b are placed close to the same chamber 15 and assembled in a series configuration, the generated magnetic field will be in phase and the plasma will be on the coils 10a, 10b Form a stable halfway between.

Improved plasma generation equipment has been designed to alleviate at least some of the problems mentioned above.

Summary of the invention According to the present invention, there is provided a plasma generating apparatus including a plurality of plasma sources, each plasma source including a separate antenna coil assembly electrically coupled to a common electrical terminal via a separate transmission line, each transmission line Assembled to transmit an RF electrical power signal from the common electrical terminal to the respective antenna coil assembly, where each transmission line includes a length that is an odd multiple of ¼ of the wavelength of the RF electrical power signal.

The plasma generating device forces the sharing of electrical power to each plasma source so that each source can generate stable plasma local to its respective location on the plasma chamber.

In an embodiment, each transmission line includes a length that is substantially a quarter of a wavelength of the RF electrical power signal.

In an embodiment, each plasma source is electrically connected together in a parallel configuration.

In an embodiment, at least one transmission line of the device includes an impedance matching circuit for matching the electrical impedance of the respective antenna coil assembly and the common electrical terminal. The impedance matching circuit may include an inductor and a capacitor. These inductors and capacitors can be configured into a π network configuration. In an embodiment, the impedance matching circuit includes a quarter-wave impedance transformer.

In an embodiment, each transmission line of the device includes an impedance matching circuit for matching the electrical impedance of the respective antenna coil assembly and the common electrical terminal. Each impedance matching circuit may include inductors and capacitors, which may be configured in a π network configuration.

In an embodiment, each transmission line may further include a feeder line such as a coaxial cable for communicating the electrical power signal to the respective antenna coil assembly. The feeder can be placed between the respective impedance matching circuit and the antenna coil assembly.

In an embodiment, each antenna coil assembly includes an antenna coil and an electric resonator circuit. The electric resonator circuit includes a capacitor electrically coupled to the respective antenna coils in a parallel configuration. The antenna coil can be placed on a common plasma chamber positioned for each coil, for generating separate plasma in the same chamber. Alternatively, the antenna coils can be placed on separate plasma chambers for generating a plasma in each separate chamber.

In an embodiment, the device further includes a radio frequency electrical power supply for supplying radio frequency electrical power to the common electrical terminal. Therefore, a single electrical power supply can be used to power several separate plasma sources.

In an embodiment, the device includes an additional impedance matching circuit for matching an electrical impedance of the common electrical terminal to an RF electrical power supply.

Although the invention has been described above, it extends to any inventive combination of features stated above or in the following description. Although the illustrative embodiments of the present invention are described in detail herein with reference to the accompanying drawings, it should be understood that the present invention is not limited to such precise embodiments.

Furthermore, it is expected that a particular feature described individually or as part of an embodiment may be combined with other individually described features or parts of other embodiments, even if other features and embodiments do not mention that particular feature. Therefore, the present invention extends to these specific combinations that have not been described.

Detailed description of the preferred embodiment Referring to FIG. 2 of the drawings, a schematic illustration of a plasma generating apparatus 100 according to an embodiment of the present invention is provided. The illustrated device contains two plasma sources 110, 120, each associated with a separate plasma chamber 130, such as a plasma tube containing a gas such as nitrogen. However, each plasma source may instead be associated with a common plasma chamber. Furthermore, although the illustrated embodiment contains only two plasma sources, it should be understood that the device can be scaled up to include additional plasma sources that operate to form a single RF power supply.

The plasma sources 110, 120 are electrically coupled in a parallel configuration via respective transmission lines 140, 150. Each transmission line 140, 150 is electrically connected to a common electrical terminal 160 or node at one end and to the respective antenna coil assembly 170, 180 at the other end, and the antenna coil assembly 170, 180 are each configured to The plasma 200 is electromagnetically induced in the chamber 130 where the coils 170 and 180 are local. The plasma sources 110, 120 and therefore the antenna coil assemblies 170, 180 are powered using a radio frequency (RF) electric power source 190 electrically coupled to the common node 160. In this regard, a single RF power supply 190 is configured to power multiple plasma sources 110, 120.

The transmission lines 140, 150 coupling the antenna coil assemblies 170, 180 to the common node 160 are sized to correspond to an odd multiple of ¼ of the wavelength of the electrical power signal from the RF source 190, and in the preferred embodiment, each A transmission line 140, 150 includes an effective path length that is substantially a quarter of a wavelength of an electrical power signal to produce a phase change of π/2 radians when traversing the transmission line 140, 150. In general, the plasma source has a negative resistance characteristic and therefore if the plasma source is placed in a parallel configuration, positive feedback causes one of the coils to receive all electrical power and becomes dominant at the expense of the other coils. However, by electrically coupling each antenna coil assembly 170, 180 to a common electrical node 160 such that each assembly 170, 180 is a quarter of a wavelength from node 160, this effectively enables the coil 170 and 180 behave as if they were configured in electrical series configuration. In this situation, the effective input impedance (Z) of the transmission lines 140, 150 can be expressed as Z = Z ₀ ² /Z _L , where Z ₀ is the characteristic impedance of the transmission line and Z _L is the respective antenna coil assembly 170, 180 impedance. Therefore, if the plasma associated with the specific plasma source 110, 120 of the device begins to extinguish, Z _L will begin to increase, thereby reducing the effective impedance of the transmission lines 140, 150. The reduced impedance causes electrical power to be attracted away from other plasma sources to maintain the plasma, and thus provides stable negative feedback.

In order to maximize the electrical coupling of power from the transmission lines 140, 150 to the individual antenna coil assemblies 170, 180, the impedance of the transmission lines 140, 150 must match the impedance of the individual antenna coil assemblies 170, 180. The characteristic impedance of the coaxial cable transmission line is usually 50Ω, and therefore assuming that the antenna coil assemblies 170, 180 contain similar impedances, the electric power reflected at the coupling with the respective antenna coil assemblies 170, 180 will be minimized. At the common RF frequency of 13.56 MHz used in the plasma reactor, the ¼ wavelength is about 4 m. However, if the antenna coil assembly 170, 180 contains an impedance that is significantly different from the transmission line 140, 150 or requires a shorter cable length, the shorter cable can use a low-pass π network or a circuit and a coaxial cable The "lumped" equivalent circuit combination is illustrated in Figure 3 of the equation to customize the impedance of the transmission line.

For example, referring to FIG. 3 of the drawings, each transmission line 140, 150 includes a series configuration of a pi network 141, 151 and feeders 142, 152 such as coaxial cables for coupling electrical power from a common node 160 to respective antenna coils Assembly 170, 180. The π network 141, 151 includes inductors 143, 153 arranged in series with the feeders 142, 152, and two capacitors 144, 154 individually arranged in either side of the inductors 143, 153 in a parallel configuration. In the case where the antenna coil assembly 170, 180 includes an impedance that does not match the transmission lines 140, 150, the effective impedance of the transmission lines 140, 150 (that is, the combined impedance of the π network 141, 151 and the feed lines 142, 152) can be borrowed It is selected by selecting appropriate inductance and capacitance values for the inductors 143 and 153 and the capacitors 144 and 154, respectively.

Each antenna coil assembly 170, 180 includes coupling coils 171, 181 that extend close to the plasma chamber 130, such as a plasma tube, or can be placed on the chamber 130 and through associated electrical resonators The respective capacitors 172, 182 of the circuits 173, 183 are tuned to parallel resonance. Quarter-wavelength transmission lines 140, 150 are formed by respective π networks 141, 151 and feed lines 142, 152 and are configured to produce a π/2 radian phase shift across the line. The phase shift across the feeders 142, 152 is defined as length/(wavelength X feeder speed factor). For a typical feeder such as RG213, the speed factor Vp is 0.66. Therefore, a 1 m long RG213 feeder supporting electrical signals at a frequency (f) of 13.56 MHz will produce a phase shift of 24 ⁰ (approximately 2π/15 radians). The remaining phase shift required to generate a 90 ⁰ shift from the π network is therefore 66 ⁰ .

For a low-pass π network, the inductance (L) is defined as (Z ₀ sinθ)/ω, where ω=2 π f is the angular frequency and the capacitance (C) for each capacitor is (1-Cosθ)/ωZ ₀ sinθ . Accordingly, in order to generate additional phase shift of ^660, an inductor and capacitor to the desired inductance and capacitance values were calculated as 532nH and 150pF.

The RF power supply 190 is further impedance-matched to the common node 160 via respective impedance matching circuits 191. The impedance matching circuit 191 includes an inductor 192 and a capacitor 193. The inductor 192 is coupled to the RF power source 190 and the common node 160 in a series configuration, and the capacitor 193 is coupled between the RF source 190 and the inductor 192 in a parallel configuration.

In practice, the present invention was tested using two parallel cylindrical water-cooled plasma tubes made of Al ₂ O ₃ with similar multi-turn coil antennas. This is shown schematically in FIG. 2. Both plasma sources 110 and 120 are fed from a single 13.56MHz power supply using a common pump, which operates at ~2kW under 4Torr pressure of N2. The voltage is monitored using an oscilloscope.

Referring to Figure 4 of the drawings, an instrument display 300 showing changes in voltage across each plasma source over time is shown. 4a and 4b illustrate the voltage across each plasma source 110, 120 during the plasma ignition sequence. Fig. 4a illustrates the voltage variation on a relatively coarse time scale (20ms/div), and from this figure it is clear that the two plasma sources 110, 120 generate different plasmas at almost the same time, such as by a sudden drop in voltage As directed. Figure 4b provides a careful examination of the voltage change at the ignition point using a relatively small time scale (1ms/div). At this scale, it is obvious that the voltage across the second plasma source 120 (the lower trace in FIGS. 4a and 4b) drops and the voltage across the first plasma source 110 rises, because the second source 120 ignites first Plasma. Shortly after the plasma is ignited by the second source 120, the voltage across the first source 110 rises until the plasma also ignites close to the first source 110, thereby proving that two stable plasmas (in the same chamber 130 Or in a separate chamber) using a single power supply 190.

From the foregoing, it is therefore obvious that the plasma generating device provides a simple and effective device for generating multiple plasmas from a single power source.

10a, 10b‧‧‧‧RF antenna, coil 15‧‧‧Low pressure process chamber 20‧‧‧RF power supply 25、200‧‧‧Plasma 100‧‧‧Plasma production equipment 110、120‧‧‧Plasma source 130‧‧‧ plasma chamber 140, 150‧‧‧ transmission line 141, 151‧‧‧π network 142, 152‧‧‧ feeder 143, 153, 192 144, 154, 172, 182, 193‧‧‧ capacitor 160‧‧‧Common electrical terminal/common node 170, 180‧‧‧ antenna coil assembly 171,181‧‧‧Coupling coil 173、183‧‧‧Electric resonator circuit 190‧‧‧radio frequency (RF) electric power source/RF power supply 191‧‧‧ impedance matching circuit 300‧‧‧ instrument display

The present invention can be implemented in various ways and by examples only, and embodiments thereof will be described with reference to the accompanying drawings, in which: FIG. 1 is a schematic illustration of a known plasma generating device including two antenna coils for generating plasma in a plasma chamber, the antenna is configured in (a) series configuration and (b) parallel configuration; 2 is a schematic illustration of a plasma generating device according to an embodiment of the invention; 3 is a circuit diagram illustrating the electrical component of the embodiment illustrated in FIG. 1 with the plasma chamber removed; Figure 4a is a view of an instrument display showing the change in voltage across each plasma source with time during the ignition of the plasma, where the time scale represents a 20 ms partition; and Figure 4b is a view of an instrument display showing the change in voltage across each plasma source as a function of time during the ignition of the plasma, where the time scale represents a 1 ms partition.

200‧‧‧Plasma

100‧‧‧Plasma production equipment

110、120‧‧‧Plasma source

130‧‧‧ plasma chamber

140, 150‧‧‧ transmission line

160‧‧‧Common electrical terminal/common node

170, 180‧‧‧ antenna coil assembly

171,181‧‧‧Coupling coil

190‧‧‧radio frequency (RF) electric power source/RF power supply

191‧‧‧ impedance matching circuit

Claims (15)

A plasma generating device includes a plurality of plasma sources, each plasma source includes a separate antenna coil assembly electrically coupled to a common electrical terminal via a separate transmission line, and each transmission line is An RF electrical power signal is transmitted from the common electrical terminal to the respective antenna coil assembly, wherein each transmission line includes a length that is an odd multiple of ¼ of the wavelength of the RF electrical power signal. The plasma generating apparatus of claim 1, wherein each transmission line includes a length which is substantially a quarter of a wavelength of the radio frequency electrical power signal. As in the plasma generation equipment of claim 1 or 2, each plasma source is electrically connected together in a parallel configuration. The plasma generating device according to any one of claims 1 to 3, wherein at least one transmission line of the device includes an impedance matching circuit for impedance of the respective antenna coil assembly and the common The electrical terminals are matched. The plasma generating apparatus according to any one of claims 1 to 4, wherein each transmission line of the apparatus includes an impedance matching circuit for impedance of the respective antenna coil assembly and the common The electrical terminals are matched. The plasma generating apparatus according to claim 4 or 5, wherein the at least one or each impedance matching circuit may include an inductor and a capacitor. The plasma generating apparatus of claim 6, wherein the inductors and capacitors are configured in a π network configuration. The plasma generating apparatus according to any one of claims 1 to 7, wherein each transmission line further includes a feeder for transmitting the electric power signal to the respective antenna coil assembly. The plasma generating apparatus according to claim 8, wherein the feeder line is disposed between the respective impedance matching circuit and the antenna coil assembly. The plasma generating apparatus according to any one of claims 1 to 9, wherein each antenna coil assembly includes an antenna coil and an electric resonator circuit. The plasma generating apparatus of claim 10, wherein the electric resonator circuit includes a capacitor electrically coupled to the respective antenna coils in a parallel configuration. The plasma generating apparatus according to claim 10 or 11, further comprising a plasma chamber, wherein each antenna coil is disposed on the plasma chamber positioned for each coil, for generating a separate Plasma. The plasma generating apparatus according to claim 10 or 11, further comprising a plurality of plasma chambers, wherein each antenna coil is disposed on a separate plasma chamber for generating a plasma in each chamber. The plasma generating apparatus according to any one of claims 1 to 13, further comprising a radio frequency electrical power supply for supplying radio frequency electrical power to the common electrical terminal. The plasma generating apparatus of claim 14, further comprising an impedance matching circuit for matching the electrical impedance of one of the common electrical terminals to the radio frequency electric power supply.

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